The present invention relates to a process for recovering molybdenum from ammoniacal leach liquors. There are many hydrometallurgical processes in which low levels of molybdenum values remain in the raffinate after other metal values have been removed. One example of such a process is the "cuprion" process disclosed in U.S. Pat. No. 3,983,017 to Lester Szabo entitled "Recovery of Metal Values From Manganese Deep Sea Nodules Using Ammoniacal Cuprous Leach Solutions." The teachings of this patent are incorporated herein by reference.
In that process, manganese nodules are leached. The major metals of interest are copper and nickel; however, cobalt and molybdenum values are also solubilized in the ammoniacal leach liquor used. Indeed, in that process, the solubilized copper and nickel values are extracted from the leach liquor leaving molybdenum and cobalt in the raffinate. The present invention may be used to recover the molybdenum values from this type of raffinate.
Another source of molybdenum-containing ammoniacal leach liquors is from certain copper in-situ mining systems. An example of such an in-situ system is disclosed in U.S. patent application Ser. No. 724,548 entitled "In-Situ Mining Method and apparatus," the teachings of which are incorporated herein by reference.
The recovery of molybdenum from ammoniacal leach liquors obtained during in-situ mining and the cuprion process has met with severe economic constraints. These problems are due to the fact that it is difficult to extract molybdenum when present in low concentrations from an ammoniacal liquor. Although molybdenum may be selectively extracted from acidic solutions, the concentration of molybdenum present in these processes does not justify adding enough acid to convert the basic leach liquor into an acidic leach liquor. At this point, it is emphasized that economical recovery of molybdenum from acidic leach liquors is well known, and, in particular, amines can be utilized to extract molybdenum as a molybdate anion from acidic leach liquors. Once the molybdenum is loaded onto an amine, it can be stripped from the amine with ammonia.
Typical extractants for molybdenum include Alamine 336 which is a tertiary amine sold by General Mills and having the formula: EQU R.sub.3 N where R=C.sub.8 -C.sub.10
and Aliquot 336 which is a quarternary ammonium salt sold by General Mills having the formula (R.sub.3 N.sup.+ CH.sub.3)Cl.sup.- where R=C.sub.8 -C.sub.10 (methyl tricaprylyl ammonium chloride).